Decius Marinus Venantius
Basilius, of consular rank, most illustrious Prefect
of the City,
patricius, ordinary consul
after the field and the
podium
had been toppled by an earthquake
— from which God save us —
restored them at his own expense.

Most appropriately, this inscription, one of a pair found in the early 19c, has been reërected in a place of honor in the W entrance of the amphitheater. Every visitor passes by them, although few stop to read.

A nearby informational plaque told me that Basilius was consul in A.D. 484; the article
"Amphitheatrum Flavium"
of Platner's Topography of Ancient Rome puts his consulate in 508, if with some doubt.

As for the text itself, "ordinary" and "patrician" look like they pull in opposite directions. Both of these are technical terms, however: patricius is an honorific adjective (at this period,
no longer what a "patrician" had been in the days of the republic), and "ordinary consul" means one of the proper consuls for the whole year, whose term of office started on the Kalends of January, and after whom the year was named — as opposed to "suffect consuls", who 'made up' (sub-facere) the other guy's term. This could happen for several reasons: in the early Republic, it was because an ordinary consul had died in office.

Each modifier is thus a sort of badge of honor, as is "vir consularis" — even if under the Empire, it did not necessarily mean, as it did earlier, that you had been a consul. On the other hand, this man needs no added honorifics: he was Prefect of the City, about as close to emperor as you could get; and by 484 (or 508), there was no emperor, even. . . .

So even post-imperial Christian Rome felt the need to restore its amphitheatre and set up inscriptions modeled on a type at least 600 years old.

Look carefully at the inscription, however, and you will see the Middle Ages creeping up on us: the lines over inl, praef and vrb are a new development. They will rapidly become the standard medieval method of indicating an abbreviation, although the rules will change: by and large, medieval usage uses this sign to mean that letters have been skipped within a word; here it is applied to words that are merely truncated.

Images with borders lead to more information.
The thicker the border, the more information.
(Details here.)